This invention relates generally as indicated to a slip-fit transformer stud electrical connector, and more particularly, a connector which accommodates in the same slip-fit hole two different transformer stud sizes.
This invention relates to certain improvements in transformer stud electrical connectors as shown in the copending application of David R. Fillinger, Ser. No. 08,502,830, filed Jul. 14, 1995, and entitled xe2x80x9cTransformer Stud Electrical Connectorxe2x80x9d now U.S. Pat. No. 5,690,516.
In power distribution, transformers are provided with extending threaded studs which are usually copper. Stud connectors are secured to such studs and a number of conductors are in turn secured to the connectors. Typically, the stud connector has an elongated body of conductive material such as aluminum with a stud receiving hole in one end and a plurality of transverse holes or ports in which the conductors are clamped by set screws, for example. The bottoms of the holes or ports form pads against which the conductors are clamped by the set screws.
For many years transformer stud connectors have been supplied in two styles: the slip-fit and the screw-on. The screw-on version has an internal thread in the connector matching the thread on the transformer stud and is installed by rotating the connector onto the threaded stud. Since the stud is of considerable length, a large number of revolutions of the connector is required to seat and lock the connector on the stud. The exact position of the connector on the stud usually requires the tightening of a lock nut against the connector.
The slip-fit usually has an oversized threaded hole compared to the stud diameter. The connector is installed by sliding the oversized connector over the threaded stud and tightening a jam screw from the top side of the connector to force the internal and external threads to mesh. The contact area is less than a perfect fit since the diameters do not match and the threads between the stud and connector do not completely seat. Moreover, the contact between the stud and the connector occurs only along a very narrow strip along the bottom of the stud. Also, as a result of the limited interface, the connector has a tendency to pivot when pressure is applied to the outer end of the connector, especially when additional conductors are installed.
Attempts to stabilize the connection are seen in Kraft U.S. Pat. No. 4,214,806 where the stud is forced against parallel edges to achieve a two line contact or triangular locking arrangement including the jam screw. The surface area of pressure contact is still minimal.
More recently, a stud connector sold by Erico, Inc. under the trademark SHARK(trademark), and as shown in the above noted copending application of David R. Fillinger, utilizes an oversize unthreaded hole and an intersecting smaller threaded hole with threads matching those of the stud. Opposite jam screws force the matching threads together providing good high pressure, large surface area, electrical contact with improved stability. The much larger surface area contact provides a cooler running connection avoiding heat degradation or burnout.
A major problem is that transformer studs come in two different sizes, typically ⅝xe2x80x3 and 1xe2x80x3. Earlier stud connectors were stocked in two different sizes to accommodate both stud sizes. More recently, tiered connector designs often incorporate openings for both stud sizes, with the ⅝xe2x80x3 stud opening generally located on the upper tier, and the 1xe2x80x3 stud opening located on the bottom tier. While this arrangement avoids the necessity of stocking two different connectors, it nonetheless requires that valuable space be wasted on any connector when both stud holes are present, but only one is utilized.
Another method of incorporating openings for both stud sizes involves forming the two size stud openings in opposite ends of the connector, along the axis of the conductor row. While this also eliminates the need for two separate connectors, the wasted material and space is the same. A stud hole on both ends also lengthens the connector, increasing any cantilever stress on the stud and connection.
Another problem associated with this style of connector is that the orientation of the set screws changes depending on the stud size used. Generally, connectors are referred to as either left hand or right hand in configuration, when looking at the front of the connector. In a left hand configuration, when the connector is placed on the stud, the set screws for the conductor ports are on the left hand side of the connector. Turning the connector around to utilize the opposite stud opening will usually reverse the orientation of the set screws. Thus, changing from one stud size to another may mean giving up the ability to choose the orientation of the set screws.
It would, accordingly, be desirable to have a connector which combines the tight fit of the screw-on connection with the easier and quicker installation of the slip-fit connector, while at the same time providing a much improved electrical connection in the same single slip-fit hole for two different size transformer studs.
The present invention accommodates both stud sizes in a single opening. The hole is formed using at least three centers, with the centers aligned usually vertically. The diameters formed on the centers are each of a different size. The largest opening is the clearance opening, designed to allow insertion of a 1-14 threaded stud. The intermediate opening incorporates a 1-14 threaded, semicircular opening with the center sharing the same vertical axis as the first opening, but located slightly below or offset the center of the larger opening. The third opening incorporates a ⅝-11 threaded hole, with the center again sharing a common vertical alignment, but located slightly lower than or offset from the second center. In this manner, a single stepped opening accommodates either stud size, while simultaneously allowing sufficient surface area or thread engagement to ensure both a rigid and firm physical connection and a good electrical connection for either size stud.
The invention then provides a transformer stud electrical connector which has an electrically conducting connector body having a blind stud receiving hole which will accommodate at least two different size studs, the hole having circumference arcs formed by arcs having at least three centers, and each of a different radius. The centers of the arcs are offset from each other yet aligned, normally vertically. One or more jam screws have an axis on the alignment and force an inserted stud into one or another of the arcs formed by the smaller radii. The smaller radii arcs are respectively threaded to match the threads on the respective studs accommodated. The intermediate radius forms two arcs, with the arc formed by a smaller radius positioned between the two arcs, and bisecting the intermediate radius arcs. The connector is formed by drilling the blind stud receiving hole on the at least three centers which are aligned with the axis of the jam screw hole or holes. Threads are then formed on all but the largest hole surface which match the threads of the different studs.
One significant advantage of the invention is that no material is wasted on a second stud opening, permitting for a shorter, lighter connector, which reduces the cantilever stress on the transformer stud. Another benefit is that it permits the same set screw orientation regardless of stud size being utilized. They do not have to be turned end-for-end. Connectors are supplied in either a left hand or right hand configuration, regardless of required stud size, and the orientation of the set screws remains the same for either stud.
This invention is useful on any style of stud connector, wherever an application exists for different stud sizes.
To the accomplishment of the foregoing and related ends, the invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.